Aircraft transmissions for helicopters, turboprops and geared turbofan aircraft require high reliability and provide several thousand hours of operation between overhauls. In addition, They should be lightweight and have very high efficiency to minimize operating costs for the aircraft.

Today gear drive operations have several options when selecting the proper lubricant for their gearboxes. As in the past, the primary lubricant used for gearbox lubrication is mineral oil. But with the advances in technology, synthetic hydrocarbons (PAOs) and polyglycols show very specific advantages in certain applications. With gear drives becoming more and more precise, it is now also to the benefit of the gear operator to verify that he or she has the proper additive package and viscosity in the lubricant selected. Fig. 1 shoes that a gear oil is a combination of a base oil and specific additives. The base oils can be either mineral oil, a synthetic or even in some cases a combination of the two.

The diagnosis and prevention of gear tooth and bearing wear requires the discovery and understanding of the particular mechanism of wear, which in turn indicates the best method of prevention. Because a gearbox is a tribologically dependent mechanism, some understanding of gear and bearing tribology is essential for this process. Tribology is the general term for the study and practice of lubrication, friction and wear. If tribology is neglected or considered insignificant, poor reliability and short life will result.

This past fall, I had the opportunity to travel to Japan, Korea, Taiwan, and Singapore to witness first-hand the status of the power transmission and machine tool industries in these areas. Points of interest included equipment, material handling, computerization, wage and tax structures, inventory controls, and workforce attitude.

When it comes to purchasing gear lubricants, many people on both the sales and purchasing side decide to play the numbers game. The person with the most numbers, or the biggest numbers, or the lowest numbers, must have the best product - right? Wrong; gear oil selection is not a game, and numbers alone cannot determine the right product for an application.

Myth No. 1: Oil Is Oil. Using the wrong oil is a common cause of gear failure. Gears require lubricants blended specifically for the application. For example, slow-speed spur gears, high-speed helical gears, hypoid gears and worm gears all require different lubricants. Application parameters, such as operating speeds, transmitted loads, temperature extremes and contamination risks, must be considered when choosing an oil. Using the right oil can improve efficiency and extend gear life.

The Integral Temperature Method for the evaluation of the scoring load capacity of gears is described. All necessary equations for the practical application are presented. The limit scoring temperature for any oil can be obtained from a gear scoring test.

The following article is concerned with the analysis of the wear-reducing effect of PVD-coatings in gearings. Standardized test methods are used, which under near-real conditions enable
statements to be made about the different forms of damage and wear (micropitting, macropitting, scuffing).

This article summarizes the use of laboratory fatigue data for bearings and gears coupled with probabilistic life prediction and EHD theories to predict the life and reliability of a commercial turboprop gearbox.

The October 2011 issue of Gear Technology featured the article “Low-Distortion Heat Treatment of Transmission Components,” which covered
the combination of low-pressure
carburizing and high pressure gas quenching in an automotive environment. Here, heat treating expert Dan Herring explains why oil quenching is an appropriate choice for many applications.

A study was performed to evaluate fault detection effectiveness as applied to gear-tooth pitting-fatigue damage. Vibration and oil-debris monitoring (ODM) data were gathered from 24 sets
of spur pinion and face gears run
during a previous endurance evaluation
study.